The proposed research aims to investigate the recently discovered ovarian hormone in mosquitoes with special emphasis on its nature and role in the control of reproduction. The experiments are designed to provide essential information on the chemical nature of the hormone and to discover when and where it is synthesized. The possible role of the juvenile hormone in permitting the action of the ovarian hormone will be investigated. The role of the ovarian hormone in autogenous mosquitoes will also be studied. The ovarian hormone controls the synthesis of yolk protein by the fat body. Therefore the action of the hormone is assayed by in vitro incubation of fat body followed by a sensitive radio-immune precipitation of the synthesized yolk protein. It is anticipated that this work will pave the way for future studies on how hormones control protein synthesis in insects, on the presence and nature of ovarian hormones in other insects, and the possible use of the ovarian hormone as a biological control agent for mosquitoes.